1. Field of Invention
The present invention relates to a closed circuit control device for a scanner. More particularly, the present invention relates to a closed circuit control device that utilizes an optical meter.
2. Description of Related Art
In general, optical scanners can have two main modes of operation, namely, reflective scanning and transparency scanning. In reflective scanning, a document (the document is non-transparent) is placed on top of a transparent glass panel, and then light from a light source shines through the transparent glass panel and reflects back from the document. After passing through a set of optical lenses, the reflected light enters an optical sensor such as a charge couple device (CCD) or a contact image sensor (CIS). Ultimately, a scan image is formed. In transparency scanning, a document (the document can be a film negative or a transparency for projector) is also placed on top of a transparent glass panel. However, light from a light source has to shine through the document first. After going through the transparent glass panel, the light passes through a set of optical lenses and finally enters the optical sensor to produce a scan image.
FIG. 1 is a schematic cross-sectional side view of a conventional scanning system. To scan a non-transparent document 40, a reflective scanning system is used. A light source 38 inside a sensor box 30 emits a light ray that passes through a transparent glass panel 20. The ray of light is directed at the document 40 and then reflected back through the narrow crevice 34 into the sensor box 30. After passing through an optical system 36 (detailed structure not shown), the reflected light is transmitted to an optical sensor 32 (CCD or CIS). The optical sensor 32 then transforms the incoming light into optical data for subsequent image production, thereby completing one scanning operation. Thereafter, the sensor box 30 steps forward along the transparent glass panel to carry out more scanning operations until everything on the document 40 has been reflected and converted into image data. All through the reflective scanning operation, a light source carrier 10 located above the transparent glass panel 20 remains idle.
To carry out the scanning of a transparent document 40, a light source inside the light source carrier 10 emits a light ray that passes through a crevice 14. The light beam passes through the document 40 and the transparent glass panel 20 and then enters the sensor box 30 through its crevice 34. Similarly, the light is transmitted to the optical sensor 32 after going through the optical system 36 (detail structure not shown). The optical sensor 32 then transforms the incoming light into optical data for subsequent image production, thereby completing one scanning operation. Thereafter, the light source carrier 10 and the sensor box 30 step forward in synchrony along the transparent glass panel 20 to carry out more scanning operations until everything on the document 40 has been converted into image data. All through the transparency scanning operation, the light source 38 inside the sensor box 30 produces no light.
In a conventional scanner, whether the scanning is in reflective or transparency mode, the light source carrier and the sensor box are driven by a motor. In general, control of the motor is difficult, leading to some jerkiness of motion, that is, sometimes faster and sometimes slower. Such discontinuous motion may lead to some discontinuity in the extraction of image data and ultimately may lead to some distortion of the scanned image.
To resolve the driving problem, sensors are often installed inside a conventional scanner for monitoring the speed of carriers so that feedback signals are returned to the motor. However, the installation of sensors complicates the control circuit and increases production cost.